I would disconnect your gas peddle linkage and check if you are able to drop the idle down A body throttle cable doesn't have enough travel in the peddle I perches a secondary linkage to get full throttle part number 20-122 and a throttle lever extension modal number 4014412 to also get more...
my personal opinion is to stay away from MSD You can upgrade your ignition control box for more RPM and if you brake down it can be easily changed on the side of the road I installed a 650 on my car and it was a big improvement Just took some time to set up Just my personal opinion